Most of us have heard the cliche man is a social animal. We need to be in a group and that’s how we have been from the start. It starts and ends with family, community, tribe,caste, religion, nationality,race etc etc so it is natural to have one inclination or the other.
If not patriotism we will find something else to cling on to. At least I think that is better than racial,religious, caste- based discriminations.
I would say after family probably patriotism is the least harmful thing compared to other things I have mentioned. So in that context not overrated at all.